(1) Field of the Invention
The present invention relates to an integrated circuit device that includes a differential amplification circuit, and particularly to an improvement in the high-frequency operation of the integrated circuit device.
(2) Related Art
In recent years, active developments have been made in high-frequency integrated circuit devices for use in telecommunication equipment, aiming at further promoting broadband wireless communications. The high-frequency integrated circuit devices include circuits such as a Gilbert cell, in which a differential amplification circuit and an emitter follower are usually incorporated.
A xe2x80x9cGilbert cellxe2x80x9d has a configuration in which a circuit formed by cross-connecting two differential amplification circuits is connected in series to one differential amplification circuit. It is also called a xe2x80x9cGilbert multiplierxe2x80x9d (Paul R. Gray, Robert G. Meyer, xe2x80x9cAnalysis and Design of Analog Integrated Circuitsxe2x80x9d, John Wiley and Sons, 1977).
FIG. 1 is a circuit diagram showing a circuit configuration of a typical Gilbert cell. In FIG. 1, the Gilbert cell 1 includes input terminals T14 and T15 into which a high-frequency reception signal (an RF signal) is inputted, input terminals T12 and T13 into which a local-oscillator signal (an LO signal) is inputted, and output terminals T10 and T11 from which an intermediate frequency signal (an IF signal) that has a lower frequency is outputted.
The IF signal is generated by superimposing (a) a signal whose frequency equals to a sum of a frequency of the RF signal and a frequency of the LO signal and (b) a signal whose frequency equals to a difference between the frequency of the RF signal and the frequency of the LO signal. Note here that both the RF signal and the LO signal are balanced input, and therefore, the Gilbert cell 1 is a so-called double balanced mixer.
Transistors Tr14 and Tr15 and resistors R10 and R11 form a differential amplification circuit. The resistor R10 is connected to an emitter of the transistor Tr14 and the resistor R11 is connected to an emitter of the transistor Tr15.
This differential amplification circuit is used as a linear amplification circuit. The resistors R10 and R11 are provided to increase an input voltage range of the differential amplification circuit. Specifically, an input dynamic range of the differential amplification circuit is adjusted by appropriately selecting resistance values of the resistors R10 and R11.
Conventionally, it is common that circuit layouts of integrated circuit devices are determined based on circuit diagrams. A circuit layout of the above Gilbert cell is also determined based on a circuit diagram. FIG. 2 shows an example of a conventional circuit layout of the Gilbert cell, particularly the transistors Tr14 and Tr15, having the circuit configuration shown in FIG. 1.
As FIG. 2 shows, the transistors Tr14 and Tr15 are substantially symmetrical with respect to a dotted line L2. Also, the transistors Tr14 and Tr15 both have a multiple finger configuration, in which rectangular fingers of bases, emitters, and collectors are arranged alternately like the teeth of a comb. The fingers of the transistor Tr14 and the fingers of the transistor Tr15 are parallel to each other, and also, substantially parallel to the dotted line L2.
A collector wiring WC20 of the transistor Tr14 extends from collector fingers C20 and C21. A base wiring WB20 extends from base fingers B20, B21, and B22. An emitter wiring WE20 extends from emitter fingers E20 and E21.
The transistor Tr15 also has the same configuration as the transistor Tr14. Specifically, a base wiring WB21, a collector wiring WC21, and an emitter wiring WE21 respectively extend from base fingers B23 to B25, collector fingers C23 and C24, and emitter fingers E23 and E24.
Here, a stray capacitance is generated between the two emitter wirings WE20 and WE21. A condenser C10 in FIG. 1 is an equivalent circuit indicating this stray capacitance. To enable an electric current to flow thorough the resistors R10 and R11, an electric charge corresponding to the stray capacitance needs to be accumulated. Therefore, an operation delay corresponding to the time taken for accumulating the electric charge is inevitable. This makes it difficult for an electric current to flow through the resistors R10 and R11 at the time of high-frequency operation. Accordingly, the adjustment of an input dynamic range of the differential amplification circuit formed by the transistors Tr14 and Tr15 becomes difficult. The problem is, therefore, that the Gilbert cell 1 may not be able to achieve desired performances at the time of high-frequency operation.
Here, although FIG. 2 shows the transistors Tr14 and Tr15 each including seven fingers, the number of fingers may be increased to keep up with increased requirements of transistor performances. In this case, desired performances of the transistors may not be achieved at the time of high-frequency operation. As described above, integrated circuit devices that include a differential amplification circuit are known to suffer from various problems at the high-frequency operation. This has resulted in increasing demands for integrated circuit devices that can operate normally even in a high-frequency area.
In view of the above problems, the objective of the present invention is to provide an integrated circuit device that includes a differential amplification circuit and that can operate normally even at high frequency.
The above objective of the present invention can be achieved by an integrated circuit device, including: a first bipolar transistor; a second bipolar transistor that is positioned to be adjacent to the first bipolar transistor; a first wiring that is electrically connected to an emitter of the first bipolar transistor and extends therefrom into a direction opposite to the second bipolar transistor with respect to the first bipolar transistor; and a second wiring that is electrically connected to an emitter of the second bipolar transistor and extends therefrom into a direction opposite to the first bipolar transistor with respect to the second bipolar transistor, wherein the first bipolar transistor and the second bipolar transistor form a differential amplification circuit.
With this configuration, a stray capacity between the first emitter wiring and the second emitter wiring can be reduced, and therefore, the above-described case where an input dynamic range cannot be adjusted appropriately at the high-frequency operation can be avoided. This enables desired performances of the integrated circuit device to be achieved.
The above objective of the present invention can also be achieved by an integrated circuit device, including a Gilbert cell that includes the integrated circuit device, including: a first bipolar transistor; a second bipolar transistor that is positioned to be adjacent to the first bipolar transistor; a first wiring that is electrically connected to an emitter of the first bipolar transistor and extends therefrom into a direction opposite to the second bipolar transistor with respect to the first bipolar transistor; and a second wiring that is electrically connected to an emitter of the second bipolar transistor and extends therefrom into a direction opposite to the first bipolar transistor with respect to the second bipolar transistor, wherein the first bipolar transistor and the second bipolar transistor form a differential amplification circuit.
With this configuration, a Gilbert cell that can operate normally even at high frequency can be realized.
The above objective of the present invention can also be achieved by an integrated circuit device, including: a controlled-potential power source wiring; a first bipolar transistor; a second bipolar transistor that is positioned to be opposite to the first bipolar transistor with respect to the controlled-potential power source wiring; a third bipolar transistor that is positioned in such a manner that a collector thereof is close to a base of the first bipolar transistor and is electrically connected to the base of the first bipolar transistor and the controlled-potential power source wiring; a fourth bipolar transistor that is positioned in such a manner that a collector thereof is close to a base of the second bipolar transistor and is electrically connected to the base of the second bipolar transistor and the controlled-potential power source wiring.
With this configuration, a length of a wiring between an input terminal and an output terminal can be shortened, and the capacity of the wiring can be reduced accordingly. This enables high-frequency performances of a differential amplifier to be improved.